Apr ’14 SBI: West System Epoxy/PB Plus HDU Test Report

A look at some of the failures.

In order to assist Precision Board users everywhere, Coastal Enterprises has partnered with leading epoxy manufacturer West System to conduct physical testing on Precision Board HDU bonded with their Six10 Epoxy to determine the bond strength of several configurations and densities. The tests also included testing the pull strength of various fasteners potted into Precision Board with the same adhesive.

All testing was done to destruction, “Destruction Testing,” to show at what pressure load the bond line failed and also to show where the failure occurred. The pictures accompanying this article show dramatic results of this testing.

I designed a test protocol that would examine the effectiveness of our typical hardware bonding techniques using Six10® Adhesive. I chose Six10 primarily because of its ease of application, which I believe would be a benefit in a sign shop. I would note that using our West System ® 105 Resin with any 200 Series Hardener thickened using 406 Colloidal Silica® filler would achieve the same results and many shops keep these products on their work bench.

Each test sample consisted of four test sites:

• A lag eye-screw in a proper sized pilot hole tested in shear. • The same type lag eye-screw embedded in an over-sized hole using Six10 tested in shear. • An eyebolt with two nuts embedded in an oversized hole using Six10 tested in shear. • An eyebolt with two nuts embedded in an oversized hole using Six10 loaded in tension and pulled with our test fixture to determine a measured value for pull-out strength.

To test the samples shear, I hung twenty-pound weights, a simple dead weight load, one at a time until the HDU board failed. The following series of photos show how this work was done.

Photo 7: The 30-lb. board easily held a 140-pond load and failed shortly after loading and additional 20 pounds for a total of 160 pounds dead load. Very impressive.

Next I changed it up a bit and employed what we term as advanced hardware bonding. The idea is to use a bolt and nut set up which is very good when drilling a blind hole.

Photo 8: The cast eyebolt on the bottom of this picture illustrates the set up I used. I drilled a hole the diameter of the outside points on the nut such that the assembly can be pushed into the prefilled hole and the nuts center everything. For the 10- and 15-lb. board, I used a forged eyehook instead to the cast eyebolt shown here. The strength of the 30-lb. board forced me to install the cast eyebolt shown here—the forged eyehook simply straightened the metal out without even taxing the epoxy bond.

The technique: With the nuts off, spray the threads with Pam® Cooking spray off to the side on a paper towel, thread the nuts on as shown, fill the pre-drilled hole about half-full with Six10, and coat the exposed threads between the nuts too. Then push the assembly into the hole, clean up any squeeze out, and let it cure.

As an aside, the pine block in the photo has just such a set up, and because the threads were coated, the eyebolt goes in and out—no problem. This particular block is a prop we use when teaching hardware bonding and is over twenty years old! It has been loaded in our extraction frame forty or more times with a direct load close to two tons! And it’s still going strong.

Photo 9: This picture shows the 10-lb. board holding forty pounds using the technique I just described. Recall that the lag screw set up failed under a 40-pound load. It did fail under a sixty-pound load. Quite good for a 10-lb. board.

Although I somehow didn’t take a picture of the 15-lb. board loaded using the eyebolt, the result was very impressive. The 15-lb. board held 80 pounds and failed at 100 pounds! For a relatively low-density foam that is outstanding.

Photo 10: As good as the 15-lb. board performed, the 30-lb. board surpassed all my expectations. Shown here is the 30-lb. board holding 160 pounds–which is all the weight I had on hand! No failure at all.

Photo 11: For the final phase of testing, I again installed an eyebolt with the double nut set up and cut out a corner to load in our extraction frame as shown above. The load cell is attached to a digital readout so we can identify the tensile pull out strength of each density Precision Board.

Photos 12 and 13: The 10-lb. board failed under the load from the lever arm itself which exerts a load of 193 pounds. Nearly a 200-pound load with low-density material is still very good and fails a significant amount of the HDU foam.

Photos 14 and 15: These pictures show the 15-lb. board in the test frame and after failure. It took 396 pounds of direct tensile load to break this block.

In my first attempt to pull a forged eyebolt from the 30-lb. block at 496 pounds direct tensile load, the eyebolt straightened out. I didn’t spray any Pam on these threads so I couldn’t remove the eyebolt. I remounted another assembly with an eyebolt and two nuts, but this time I used a cast eyebolt (because it would be much stronger than a forged one).

Photos 16 and 17: These photos show how the 30-lb. block virtually exploded when finally pressed to failure at a whopping 720 pounds! Recall that I sprayed these threads so the fastener would have threaded easily in and out.

To summarize, I believe I have shown sufficient test results to say the Precision Board can be used for hanging signs and wall mounted signs with great confidence and success using any density board and any of the epoxy techniques I have outlined in this report.

All information is for research purposes only. Coastal Enterprises and West System always recommends conducting your own tests to ensure your project requirements will be met.

Coastal Enterprises offers free technical support and is happy to answer any questions you may have by calling: 800/845-0745.